The following discussion of the prior art is intended to present the invention in an appropriate technical context and allow its advantages to be properly appreciated. Unless clearly indicated to the contrary, however, reference to any prior art in this specification should not be construed as an express or implied admission that such art is widely known or forms part of common general knowledge in the field.
Manual transmissions are well known in automotive applications and have the advantages of being relatively inexpensive, easy to manufacture, lightweight, robust and efficient in terms of power transmission. However, manual transmissions demand greater skill and effort from the driver of the vehicle, who must typically coordinate the movements of a manual gearshift lever and a clutch pedal in order to change transmission ratios as and when required. Even with reasonable driver skill, the changes are not completely smooth due to the inherent interruption in power transmission from the engine to the driveline, when the clutch is disengaged. Increasingly, drivers are tending to prefer the convenience and the smoothness of automatic transmissions, which are also well known. However, automatic transmissions are typically heavier, and more complex, costly and difficult to produce, as well as being less efficient in operation.
In an attempt to address at least some of these issues, automated manual transmissions (AMTs) have also been developed. Such transmissions essentially incorporate the internal gear trains of a manual transmission, but additionally provide some form of automated control over the gear selection mechanism and/or the clutch. Transmissions of this type do provide some of the benefits of both manual and automatic transmissions, including particularly with regard to shifting automation and fuel efficiency. However, they give rise to other disadvantages, the most notable being an undesirable tendency for abrupt or “jerky” operation, as the drive torque from the engine is alternately interrupted and re-connected during each gear change. Smooth acceleration from a standing start without clutch “judder” is also typically problematic. Attempts to ameliorate this problem, for example by control algorithms dictating more clutch slip and more progressive clutch engagement, typically compromise fuel efficiency and result in rapid clutch wear. Viscous fluid coupling elements have also been used in an attempt to ameliorate this problem but again, they inherently compromise the efficiency of the transmission or the driveline.
It is an object of the present invention to overcome or substantially ameliorate one or more of the disadvantages of prior art, or at least to provide a useful alternative.